1. Field of the Invention
The invention relates to the field of bagging product units on a production line, and in particular to a method and apparatus for bagging agricultural produce pallets in preparation for modifying the atmosphere surrounding the produce inside the bag with a gas or gas mixture to retard ripening and spoilage, or to otherwise promote freshness and extend the shelf life of such produce.
2. Description of the Related Art
The ripening of agricultural produce such as tomatoes or peaches is affected by the atmosphere surrounding the produce. Many foodstuffs, such as fresh produce (e.g., strawberries, lettuce, tomatoes, cauliflower), can have their fresh condition maintained for an extended period of time by controlling the gaseous atmosphere inside the package in which they are contained. Losses during shipment and storage can be substantially decreased in this manner so that a greater percentage of fresh produce can be delivered to the consumer in acceptable condition.
Many kinds of fresh produce, a primary one being strawberries, are shipped in a quantity of boxes on a pallet base, with the entire load being enclosed by a plastic bag that is sealed to the base. U.S. Pat. No. 4,055,931, which is hereby incorporated herein by reference, discloses the providing of a special atmosphere into the containing space formed by the plastic bag by first inserting a sharp-ended nozzle through the plastic sheeting, evacuating the air inside the bag, and introducing gases into the interior. U.S. patent application Ser. No. 06/428,087, filed Sept. 29, 1982, now U.S. Pat. No. 4,821,489 entitled "Method and Apparatus for Sealing a Flexible Bag to a Pallet," by Richard F. MacLeod and Kevin J. Bolejack, assigned to the assignee of the present Application, is hereby also incorporated herein by reference. It discloses a method and apparatus described briefly as follows. Produce is stacked in one or more boxes onto a pallet base having an oversized, gasproof plastic sheeting integrally related to the pallet base upper surface. The loaded pallet is placed on a rotatable table having a generally horizontal upper surface and a plastic bag is lowered over the produce which has its lower edges located to extend partway down over the turned portions of the plastic sheeting and onto the rim of the pallet base. Two rolls of tape are mounted at different heights on vertical spindles closely adjacent the rotating table and are located so that when the tape is pulled off the spindles, the two tape strips will have an edge portion in overlapping relationship with each other. An idler roller engages the two strips of tape at two different predetermined angles joining them together in a single composite tape strip. The composite tape strip is applied by a pressure roller along the lower edge of the plastic bag and the upturned plastic sheeting edge. After a full revolution of the table is completed, the tape is cut and the bag is completely sealed to the plastic sheeting. A lever arm on the pressure roller is spring-loaded so as to maintain the tape compressingly contacting the plastic bag and pallet throughout the full range of table rotation. Once the bag has been sealed, a sharp-ended nozzle punctures the bag, the bag is evacuated to remove residual air, and a prescribed pressurized gas is injected into the bag. The nozzle is then removed and the opening in the bag is taped closed.
The present approach taken in that part of the process involving securing the plastic bag over the produce and onto the pallet base has been found to be deficient in certain respects. Considerable floor space and worktime are needed in the step of slipping a plastic bag over a pallet and fastening its edges to the plastic sheeting of the pallet base. A bag must first be prepared for slipping over the pallet by expanding it to an open shape into which the pallet can enter as the bag is pulled downward over it. This is done by walking the bag around the room to fill it with air before it can be slipped over the top of the loaded pallet, and requires an appropriate amount of floor space. Two workers are required to manipulate the bag in opening it up, placing it with its opening facing downward above the top of the pallet, sliding it downward over the full height of the pallet, and smoothing and arranging the free edges of the bag in relation to the plastic pallet sheeting preparatory to the taping and sealing carried out in the next stage of the process. Using the present system about 15 pallets can be bagged, gassed, and sealed in roughly 45 minutes utilizing at least ten workers. It would be an advance in the art of produce preservation and packaging if the amount of space required for the operation, the number of personnel needed, and the time it takes could all be reduced.